The present invention relates generally to monitoring and controlling formation of organic layers by physical vapor deposition in making organic light-emitting devices.
An organic light-emitting device, also referred to as an organic electroluminescent device, can be constructed by sandwiching two or more organic layers between first and second electrodes.
In a passive matrix organic light-emitting device of conventional construction, a plurality of laterally spaced light-transmissive anodes, for example indium-tin-oxide (ITO) anodes are formed as first electrodes on a light-transmissive substrate such as, for example, a glass substrate. Two or more organic layers are then formed successively by vapor deposition of respective organic materials from respective sources, within a chamber held at reduced pressure, typically less than 10xe2x88x923 Torr. A plurality of laterally spaced cathodes are deposited as second electrodes over an uppermost one of the organic layers. The cathodes are oriented at an angle, typically at a right angle, with respect to the anodes.
Such conventional passive matrix organic light-emitting devices are operated by applying an electrical potential (also referred to as a drive voltage) between an individual row (cathode) and, sequentially, each column (anode). When a cathode is biased negatively with respect to an anode, light is emitted from a pixel defined by an overlap area of the cathode and the anode, and emitted light reaches an observer through the anode and the substrate.
In an active matrix organic light-emitting device, an array of anodes are provided as first electrodes by thin-film transistors (TFTS) which are connected to a respective light-transmissive portion. Two or more organic layers are formed successively by vapor deposition in a manner substantially equivalent to the construction of the aforementioned passive matrix device. A common cathode is deposited as a second electrode over an uppermost one of the organic layers. The construction and function of an active matrix organic light-emitting device is described in U.S. Pat. No. 5,550,066, the disclosure of which is herein incorporated by reference.
Organic materials, thicknesses of vapor-deposited organic layers, and layer configurations, useful in constructing an organic light-emitting device, are described, for example, in U.S. Pat. Nos. 4,356,429; 4,539,507; 4,720,432; and 4,769,292, the disclosures of which are herein incorporated by reference.
In order to provide an organic light-emitting device which is substantially defect-free, i.e. free of non-emitting dark defects or of highly emitting bright defects, the formation of organic layers of the device has to be monitored or controlled. Such control of vapor deposition of organic layers by sublimation or evaporation of organic material from a source is typically achieved by positioning a monitor device within the same vapor deposition zone in which the substrate or structure is to be coated with the organic layer. Thus, the monitor device receives an organic layer at the same time as the organic layer is being formed on the substrate or structure. The monitor device, in turn, provides an electrical signal which is responsive to a rate at which the organic layer is being formed on the monitor device and, therefore, related to a rate at which the organic layer is being formed on the substrate or structure which will provide the organic light-emitting device. The electrical signal of the monitor device is processed and/or amplified, and is used to control the rate of vapor deposition and the thickness of the organic layer being formed on the device substrate or structure by adjusting a vapor source temperature control element, such as, for example, a source heater.
Well-known monitor devices are so-called crystal mass-sensor devices in which the monitor is a quartz crystal having two opposing electrodes. The crystal is part of an oscillator circuit provided in a deposition rate monitor. Within an acceptable range, a frequency of oscillation of the oscillator circuit is approximately inversely proportional to a mass-loading on a surface of the crystal occasioned by a layer or by multiple layers of material deposited on the crystal. When the acceptable range of mass-loading of the crystal is exceeded, for example by build-up of an excess number of deposited layers, the oscillator circuit can no longer function reliably, necessitating replacement of the xe2x80x9coverloadedxe2x80x9d crystal with a new crystal mass-sensor. Such replacement, in turn, requires discontinuation of the vapor deposition process.
In addition, when certain organic layers are deposited onto crystal mass-sensor devices there can be a tendency for the layers to start cracking and flaking from the mass sensor surface after coating thickness build-up on the order of 500-2,000 nanometer (nm). This can cause the crystal mass-sensor to become inaccurate in its coating rate measurement capability at thicknesses well below the aforementioned mass loading limit.
In development efforts, several organic light-emitting devices can typically be prepared before a crystal mass-sensor must be replaced due to excessive mass-loading or cracking and flaking of deposited layers. This does not present a problem in such efforts, since other considerations usually require disruption of vapor deposition by opening the deposition chamber for manual replacement of substrates or structures, replenishment of organic material in relatively small vapor sources, and the like.
However, in a manufacturing environment, designed for repeatedly making a relatively large number of organic light-emitting devices, replacement of xe2x80x9coverloadedxe2x80x9d crystal mass-sensors or of crystal mass-sensors having cracked or flaking organic layers would constitute a serious limitation because a manufacturing system is configured in all aspects to provide the capacity of producing all organic layers on numerous device structures and, indeed, to produce fully encapsulated organic light-emitting devices.
It is therefore an object of the present invention to efficiently deposit an evaporated or sublimed organic layer onto a structure which will form part of an organic light-emitting device.
This object is achieved by an apparatus for depositing an evaporated or sublimed organic layer onto a structure which will provide part of an organic light-emitting device, comprising:
a) a housing defining a chamber and a pump connected to the chamber for reducing the pressure therein;
b) a source for receiving organic material to be evaporated or sublimed and means connected to the source for adjusting the temperature thereof to control the rate at which the organic material is evaporated or sublimed;
c) means for positioning the structure so that such structure is located spaced from the source in a deposition zone;
d) a moving member moving through a plurality of positions along a path of motion;
e) the moving member in a first position having a portion thereof positioned in the deposition zone for receiving organic material from the source at the same time such organic material is deposited onto the structure;
f) first optical sensing means in a second position disposed relative to the moving member outside the deposition zone for sensing a thickness of the organic material deposited on the portion of the moving member;
g) electrical means connected to the first optical sensing means and responsive to the thickness of the organic material sensed by the first optical sensing means;
h) means for adjusting the temperature control means to control the rate of deposition and the thickness of the organic layer formed on the structure; and
i) cleaning means disposed in a third position along the path of motion of the member outside the deposition zone beyond the first optical sensing means for removing in whole or in part organic material deposited on the portion of the member so that such portion can be reused in the deposition zone.